The association between independent predictors and outcome was assessed by comparing the follow-up data with a Cox proportional hazards regression model. The assumption of the proportionality of risk during the observation time, has been evaluated using the analysis of residues of Schoenfeld. Deaths from causes unrelated to the SBI were treated as censored observations. The distribution of the time function of the events was analysed using the method of Kaplan-Meier. The prognostic information is presented as relative risk with 95% confidence limits. Descriptive statistics are expressed as the mean value ± standard deviation. Probability values <0.05 are considered statistically significant.